The Dynafit Interchangeable U-Spring for the Superlite 150 in Z6 is the sprung U shaped fork inside the binding heel that holds the two heel pins. Its spring rate sets the binding's vertical release band, and Dynafit sell it as an interchangeable part so that band can be changed without replacing the heel.

• Sets the vertical release band: the fork is the component that determines how the heel releases forwards, and Z6 is the lower of the available bands.
• Swap instead of replace: changing the fork changes the binding's release characteristic without a new heel unit.
• Superlite 150 only: Dynafit's forks are specific to their binding, and a 150 fork must never be fitted to a Superlite 175 heel or the reverse.
• Sold in pairs: one per ski.